1. Field of the Invention
The present invention relates to cooling high power integrated circuits; and particularly to microchannel cooling of integrated circuits bonded face down on circuit boards, such as by flip-chip bonding.
2. Description of the Related Art
Many computer systems rely on so-called flip-chip bonding of die for electrical and mechanical attachment of integrated circuit chips to circuit boards. See, Goldman, et al., "Area Array Solder Interconnections for VLSI", SOLID STATE TECHNOLOGY, June, 1983, pp. 91-97. In flip-chip bonds, the integrated circuits are mounted face down on the circuit board. Solder bumps are coupled to bonding sites on the integrated circuits and corresponding bonding sites on the circuit board. The principal advantages of flip-chip bonding are a relative lack of electrical parasitics associated with the electrical connection, relatively high I/O available (in principal, at least), and repairability by removal and replacement of the chips. On the other hand, a significant difficulty is encountered in cooling flip-chip mounted chips. The solder bumps cover only a small fraction of the surface of the chip, and the underlying circuit boards are usually poor thermal conductors.
Heat is removed from commercial flip-chip systems using so-called thermal conduction module or TCM, such as described in the Goldman, et al. article cited above. However, the thermal conduction modules are very complex mechanically, and can only remove limited amounts of heat. As the power dissipated by integrated circuits increases, it is expected that the thermal conduction module technology will be insufficient.
One integrated circuit cooling technology which is capable of removing large amounts of heat is known as microchannel cooling. Microchannel cooling is described in detail in Tuckerman, et al., "High-Performance Heat Sinking for VLSI", IEEE ELECTRON DEVICE LETTERS, Vol. EDL-2, No. 5, May, 1981, pp. 126-129; Tuckerman, et al., U.S. Pat. No. 4,450,472; and Phillips, et al., U.S. Pat. No. 4,894,790.
Other microchannel cooling background is found in Goldberg, U.S. Pat. No. 4,489,363; and Goldberg, "Narrow Channel Forced Air Heat Sink", IEEE TRANSACTIONS ON COMPONENTS, HYBRIDS, AND MANUFACTURING TECHNOLOGY, Vol. CHMT-7, No. 1, March, 1984, pp. 154-159.
It has been proposed to apply microchannel type cooling to flip-chip bonded integrated circuits by Yamada, et al., U.S. Pat. No. 4,686,606. According to Yamada, et al., a grooved cooling module is bonded to a suction plate. The cooling module is coupled through a bellows-type tube to a manifold for delivering coolant to the structure. The suction plate contacts the backside of the integrated circuits through a silicone oil or other liquid, providing a suction joint at which the integrated circuit may be separated from the cooling structure.
The Yamada, et al. structure illustrates the mechanical complexity of supplying a flow of coolant through a microchannel structure that is in close thermal contact with an integrated circuit chip mounted face down on a circuit board. The integrated circuit chips will not lie perfectly flat on the circuit board, and will lay at varying heights, due to the manufacturing tolerances of flip-chip bonding. Thus, Yamada, et al. has devised this suction plate approach to making a good thermal contact with the chip. However, the suction plate envisioned by Yamada, et al requires use of a liquid which is a poor conductor of heat (in the case of oil) or which can contaminate and electrically short circuit the integrated circuits (in the case of liquid metals), and is believed to have other limitations which render it impractical.
It is desirable to provide a practical technique for applying microchannel cooling to flip-chip bonded integrated circuits, that allows for removal and replacement of individual chips, while taking advantage of the high efficiencies of microchannels in good thermal communication with the integrated circuit chips.